Abstract 384: Tumor Necrosis Factor-alpha Antagonism Attenuates Hypertension and Renal Injury Induced by Chronic Blockade of Nitric Oxide and High Salt Intake in Mice

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Earlier, we demonstrated that systemic blockade of nitric oxide (NO) generation by acute infusion of nitro-L-arginine methyl ester (L-NAME) in mice increases plasma and renal levels of tumor necrosis factor-alpha (TNF-α). In the present study, we examined the role of TNF-α in mediating hypertension and renal injury responses to chronic NO blockade by evaluating the responses to chronic administration of L-NAME (0.05 μg/g/min; by osmotic mini-pump) for 3 wks in mice (C57BL6) treated with or without TNF-α receptor antagonist, etanercept (ETN; 5 mg, ip, every alternate day). These mice were given either normal (NS; 0.03% NaCl) or high salt (HS; 4% NaCl) containing diets. Systemic blood pressure (BP) was measured by tail-cuff plethysmography. At the end of the experimental period, mice were sacrificed to collect plasma and renal tissue samples to measure TNF-α level by ELISA and to determine the extent of tissue injury such as glomerulosclerosis (GS; PAS staining) and renal interstitial fibrosis (RIF; Trichrome staining). L-NAME treatment caused increase in BP which was greater in HS (104±3 to 139±3 mmHg; n=6) than in NS group (96±6 to 124±6 mmHg; n=6). ETN treatment significantly attenuated this increase in BP in both L-NAME+HS (119±11 mmHg; n=6) and in L-NAME+NS (115±8 mmHg, n=6) groups. Renal tissue level of TNF-α was higher in L-NAME+NS (664±100 vs 325±73 pg/mg protein) and in L-NAME+HS (391±38 vs 114±17 pg/mg protein) groups compared to the levels in groups given NS (n=5) or HS (n=5) diet alone. However, the changes in plasma level of TNF-α due to chronic L-NAME treatment were minimal. ETN treatment lowered renal TNF-α level in L-NAME+NS (356±60 pg/mg protein) and in L-NAME+HS (259±65 pg/mg protein) groups. L-NAME treatment significantly increased GS (7.1±1.0 vs 17.9±2.3 % sclerosis area) and RIF, (1.5±0.1 vs 5.8±0.6 % fibrotic area) in HS group. However, these changes were minimal in NS group (GS, 10.3±1.0 vs 13.2±1.5 % and RIF, 1.3±0.1 vs 2.4±0.3 %). ETN treatment markedly attenuated the GS (11.8±0.4% and 11.9±0.6 %) and RIF (2.6±0.3% and 1.9±0.3%) both in L-NAME+HS and in L-NAME+NS groups. These data demonstrate that an enhancement in TNF-α activity is involved in mediating hypertension and renal injury responses to chronic NO blockade and HS intake.

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